The objective of this research is to present a set of powerful simulation, design, and characterization tools suitable for studying novel nanophotonic devices. The simulation tools include a three-dimensional finite-difference time-domain code adapted for parallel computing that allows for a wide range of simulation conditions and material properties to be studied, as well as a semi-analytical Green's function-based complex mode technique for studying loss in photonic crystal waveguides. The design tools consist of multifunctional photonic crystal-based template that has been simulated with nonlinear effects and measured experimentally, and planar slab waveguide structure that provides highly efficient second harmonic generation is a chip-scale device suitable for photonic integrated circuit applications. The characterization tool is composed of a phase-sensitive measurement system using a lock-in amplifier and high-precision optical stages, suitable for probing the optical characteristics of nanoscale devices. The high signal-to-noise ratio and phase shift data provided by the lock-in amplifier allow for accurate transmission measurements as well as a phase spectrum that contains information about the propagation behavior of the device beyond what is provided by the amplitude spectrum alone.

This thesis investigates the generation of second harmonic bulk waves in the presence of a free boundary. Second harmonic waves have proven to be useful in the field of nondestructive evaluation to detect fatigue in a material at an early stage. Since most experimental setups include a free surface, the influence of such a boundary is of significant practical interest. As a result, the objective of this research is to develop a quantitative understanding of the complete process of second harmonic generation at a free boundary. This research shows that the interaction of primary waves (with each other) in the nonlinear framework leads to the generation of second harmonic bulk waves. We distinguish between self-interaction of a single primary wave and the cross-interaction of two different primary waves. The proposed approach uses the perturbation method to solve the nonlinear equations of motion, and shows two fundamentally different solutions. In the case of resonance, the secondary waves grow with propagation distance. This is the most important practical case, since the growing amplitudes of these waves should be easier to experimentally measure. In the second, non-resonant case, the amplitudes of the secondary waves are constant. The complete process of second harmonic generation is analyzed for an incident Pand an incident SV-wave, with the primary and secondary fields given. Finally, the degenerate case of normal incidence is presented. Normal and oblique incidence are compared with regard to their feasibility in experimental setups. The specific behavior of second harmonic waves propagating in aluminum is numerically determined. These results enable a variety of physical insights and conclusions to be drawn from the analytical and numerical investigations.

Spectroscopic second-harmonic generation (SHG) and reflectance-anisotropy spectroscopy (RAS) are used to probe molecular adsorption on clean reconstructed single-domain stepped Si(001) in ultra-high vacuum (UHV). We implement a simplified bond hyperpolarizability model (SBHM) as a common microscopic analysis for SHG and RAS. Three different scenarios are studied: (i) The dissociative adsorption of molecular hydrogen on dangling bonds of D[subscript B] step-edges. (ii) Structural changes to rebonded r-D[subscript B] steps induced by exposure to atomic hydrogen. (iii) The adsorption of cyclopentene on Si(001)(2x1) terrace dimers in a [2+2] cycloaddition pathway. Using the SBHM we develop a new optical fingerprinting method to isolate, identify and monitor individual types of bonds (e.g. dimers, rebonds, dangling bonds, backbonds) and their chemical activity on a single-domain stepped Si(001) surface using nonresonant, but rotationally-anisotropic, second-harmonic generation (RA-SHG). The methods presented here will be applicable to many material systems and allow to track, in-situ and in real-time, the chemical action of adsorbates on surfaces. / text

Nonlinear coherent scattering phenomena from single nanoparticles have been recently proposed as alternative processes for fluorescence in multiphoton microscopy staining. Commonly applied nanoscale materials, however, have reached a certain limit in size dependent detection efficiency of weak nonlinear optical signals. None of the recent efforts in detection of second-harmonic generation (SHG), the lowest order nonlinear process, have been able to cross a ~40 nm size barrier for nanoparticles (NPs), thus remaining at the level of "large" nanoscatterers, even when resorting to the most sensitive detection techniques such as single-photon counting technology. As we realize now, this size limitation can be significantly lowered when replacing dielectric insulators or wide gap semiconductors by direct-gap semiconducting quantum dots (QDs). Herein, a new type of highly nonlinear nanoprobes is engineered in order to surpass above mentioned size barrier at the single nanoparticle scale. We consider two-photon resonant excitation in individual zinc-blende CdTe QDs of about 12.5 nm diameter, which provide efficient coherent SHG radiation, as high as 105 Hz, furthermore exhibiting remarkable sensitivity to spatial orientation of their octupolar crystalline lattice. Moreover, quantum confinement effects have been found to strongly contribute to the second-order nonlinear optical susceptibility χ(2) features. Quantitative characterization of the χ(2) of QDs by way of their spectral dispersion and size dependence is therefore undertaken by single particle spectroscopy and ensemble Hyper-Rayleigh Scattering (HRS) studies. We prove that under appropriate conditions, χ(2) of quantum confined semiconducting structures can significantly exceed that of bulk. Furthermore, a novel type of semiconducting hybrid rod-on-dot (RD) QDs is developed by building up on crystalline moieties of different symmetries, in order to increase their effective quadratic nonlinearity while maintaining their size close to a strong quantum confinement regime. The new complex hybrid χ(2) tensor is analyzed by interfering the susceptibilities from each component, considering different shape and point group symmetries associated to octupolar and dipolar crystalline structures. Significant SHG enhancement is consequently observed, exceeding that of mono-compound QDs, due to a coupling between two nonlinear materials and slower decoherence, which we attribute to the induced spatial charge separation upon photoexcitation.

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Histology has long recognized the intimate link between structure and function. Over centuries histologists have utilized an assortment of optical microscopy techniques to elucidate functional attributes of tissues through investigating tissue architecture. This thesis includes developments in the field of nonlinear optical microscopy for use in histology and pathology. The main contributions focused on the study of fibrillar collagen in the extracellular matrix (ECM) with polarization-dependent second harmonic generation (P-SHG) microscopy and the study of harmonophore-stained cellular nuclei with third harmonic generation (THG) microscopy. The P-SHG microscopy technique, “polarization-in, polarization-out” (PIPO), was developed to accurately determine the second-order polarization properties of thin tissue sections. The polarization instrumentation was implemented into a nonlinear optical microscope and a custom fitting algorithm extracted ratios of the second-order nonlinear susceptibility elements at every pixel of an obtained image. Hierarchical organization, at every level of structure, can contribute significantly to the macroscopic second-order polarization properties of fibrillar collagen in the ECM and quantifiable differences between the various tissue architectures were observed. A framework was developed, based on the collagen hierarchical organization, to interpret the submicron polarization properties of various tissues. Complimentary to the P-SHG study of connective tissue, the structure of hematoxylin and eosin (H&E) stained nuclei was revealed by THG microscopy. Imaging the 3D organization of nuclei was possible using the inherent optical sectioning provided by nonlinear microscopy. The origin of THG was investigated with spectrally- and temporally-resolved measurements, as well as the THG ratio method. A rather complex situation involving multiple dye complexes was revealed. The structure of dye aggregates was investigated with THG PIPO microscopy. The techniques of PIPO and harmonophore-stained harmonic generation microscopy show great potential for ultimately furthering understanding of tissue structure and function. H&E stained tissue investigations with THG microscopy has applications as a tool for cancer diagnostics. PIPO can elucidate the symmetry and organization of materials beyond tissues, including starch, nanowires, and protein crystals. In pathology, the developed collagen framework has strong implications, as collagen is recognized as playing a more active role in a number of diseases including idiopathic pulmonary fibrosis, wound repair, and tumour development and progression.

Histology has long recognized the intimate link between structure and function. Over centuries histologists have utilized an assortment of optical microscopy techniques to elucidate functional attributes of tissues through investigating tissue architecture. This thesis includes developments in the field of nonlinear optical microscopy for use in histology and pathology. The main contributions focused on the study of fibrillar collagen in the extracellular matrix (ECM) with polarization-dependent second harmonic generation (P-SHG) microscopy and the study of harmonophore-stained cellular nuclei with third harmonic generation (THG) microscopy. The P-SHG microscopy technique, “polarization-in, polarization-out” (PIPO), was developed to accurately determine the second-order polarization properties of thin tissue sections. The polarization instrumentation was implemented into a nonlinear optical microscope and a custom fitting algorithm extracted ratios of the second-order nonlinear susceptibility elements at every pixel of an obtained image. Hierarchical organization, at every level of structure, can contribute significantly to the macroscopic second-order polarization properties of fibrillar collagen in the ECM and quantifiable differences between the various tissue architectures were observed. A framework was developed, based on the collagen hierarchical organization, to interpret the submicron polarization properties of various tissues. Complimentary to the P-SHG study of connective tissue, the structure of hematoxylin and eosin (H&E) stained nuclei was revealed by THG microscopy. Imaging the 3D organization of nuclei was possible using the inherent optical sectioning provided by nonlinear microscopy. The origin of THG was investigated with spectrally- and temporally-resolved measurements, as well as the THG ratio method. A rather complex situation involving multiple dye complexes was revealed. The structure of dye aggregates was investigated with THG PIPO microscopy. The techniques of PIPO and harmonophore-stained harmonic generation microscopy show great potential for ultimately furthering understanding of tissue structure and function. H&E stained tissue investigations with THG microscopy has applications as a tool for cancer diagnostics. PIPO can elucidate the symmetry and organization of materials beyond tissues, including starch, nanowires, and protein crystals. In pathology, the developed collagen framework has strong implications, as collagen is recognized as playing a more active role in a number of diseases including idiopathic pulmonary fibrosis, wound repair, and tumour development and progression.

The nature of work conducted during the course of study towards a MSc degree focused on tunable diode laser absorption spectroscopy (TDLAS). This field involves the in-situ detection of gas constituents from low concentration samples. Specifically, I will focus on TDLAS systems utilizing practical optics, readymade electronics, and commercially available near infrared vertical cavity surface emitting lasers (VCSEL). In attempting to lower the minimum detectable concentrations of constituent gases, quantifying contributory noise sources is vital. Consequently, I seek to characterize principle noise sources of a prototypical TDLAS system in order to gain understanding of the limits that inhibit detection of trace gas concentrations. The noise sources which were focused on can be categorized as follows: source laser noise, optical noise, and detection noise. Through this work it was my goal to provide the means of achieving superior sensitivities.

[pt] Neste trabalho apresenta-se a implementação de um sistema de medição de pulsos ópticos curtos gerados por lasers semicondutores. Através de uma técnica indireta de medida, que usa a radiação de segundo harmônico gerada internamente nesses lasers, a duração dos pulsos curtos de luz é estimada. São apresentadas as principais considerações teóricas e experimentais envolvidas com a emissão de segundo harmônico em diodos lasers e são discutidas as principais limitações da técnica. Mostra-se que embora a determinação exata da duração dos pulsos exija medidas adicionais, é possível inferir com boa resolução temporal a duração de pulsos ópticos gerados nos regimes de chaveamento de ganho e mode-locking. / [en] In this work the implementation of a measurement system of short optical pulses generated by semiconductor lasers is presented. This indirect method estimates the pulse duration using the internally generated second harmonic radiation from these lasers. The main theoretical and experimental considerations related with the second harmonic emission are also presented. Although the precise pulse duration requires aditional measurements it is possible to estimate the duration of optical pulses generated by gain-switching and mode-loching regimes with good time-resolution.

Les nanocristaux à structure non-centrosymétrique présentent des propriétés optiques non linéaires prometteuses pour une utilisation en tant que marqueurs optiques en imagerie biomédicale, avec un intérêt significatif en termes de suivi sur de longues durées et de profondeur de pénétration dans les tissus biologiques. Le développement de ces marqueurs nécessite la détermination de leurs efficacités optiques non linéaires afin de pouvoir sélectionner les nanocristaux les plus prometteurs. Pour cela, la technique de diffusion Hyper-Rayleigh a été adaptée à la caractérisation de suspensions de nanoparticules (BaTiO3, KNbO3, KTP, LiNbO3 et ZnO, BiFeO3) pour lesquelles l’influence de paramètres comme la taille, la concentration ou l’état d’agrégation a été analysée et discutée. Les nanocristaux de BiFeO3 possèdent une efficacité optique non linéaire largement supérieure aux autres particules, démontrant leur potentiel pour la réalisation de nano-sondes optiques particulièrement performantes. Des mesures résolues en polarisation ont également été mises en œuvre pour déterminer les coefficients optiques non linéaires indépendants des particules étudiées. Dans ce cadre, une étude a permis de mettre en évidence l’influence de la forme des nanocristaux sur cette réponse. / Non-centrosymetric nanocrystals show promising nonlinear optical properties for being used as optical labels in bio-imaging applications, with significant interest for observations of long duration and for penetration depth into biological tissues. The development of such biomarkers requires the determination of their nonlinear optical properties to select the best potential markers. In this thesis, Hyper-Rayleigh Scattering (HRS) technique is used to determine nonlinear efficiencies of several nanocystals (BaTiO3, KNbO3, KTP, LiNbO3, ZnO and BiFeO3). These ensemble measurements have been performed on nanocrystals suspensions, for which the influence of parameters such as size, concentration and aggregation state was discussed. BiFeO3nanocrystals offer the best nonlinear optical efficiency compared to other particles, showing their potential as efficient optical biomarkers. Polarisation-resolved measurements have also been performed to retrieve individual coefficients of the nonlinear tensor of the investigated materials and influent parameters such as nanocrystals shape have been identified.